This invention is directed to a method and apparatus for interrupting large electric current against high voltage and has the potential for employing simple, economic apparatus for interruptions which formerly required more complex, sophisticated equipment. Also, current interruption occurs life expectancy.
The crossed field switch tube has been developed as a switching device which can be incorporated in a system for interrupting large DC currents, even against high voltages, and when properly applied for interrupting an AC current between its natural current zeros.
U.S. Pat. No. 3,555,960 to G.A.G. Hofmann and U.S. Pat. Nos. 3,604,977 and 3,769,537 to G.A.G. Hofmann illustrate such crossed field tube switching devices. U.S. Pat. No. 3,714,510 also to G.A.G. Hofmann further describes such a switching device in connection with a circuit breaker system.
U.S. Pat. No. Re. 27,557 to K. T. Lian and U.S. Pat. No. 3,611,031 to M. A. Lutz describe circuit breaker circuits in which such switching devices are employed.
U.S. Pat. No. 3,912,975 to W. Knauer and W. L. Dugan describes a high speed mechanical switch which was originally conceived as a shunting switch for the crossed field switch tube. The contact opening speed of this switch was found to be so high that in a suitable system it can serve as an interruptor. During the initial 200 microseconds after separation its contacts move a distance of 0.4 centimeters. This implies that with six atmospheres of SF.sub.6 as insulating gas, which has a breakdown field strength of approximately 250 kV/cm, the voltage hold-off capacity of the gap increases at a rate of 0.5 kV per microsecond during contact separation. In view of the fact that the switch has two contact gaps in series, the total voltage recovery capability is 1.0 kV per microsecond. It has been discovered that such a switch, properly actuated and installed with an auxiliary circuit can interrupt large currents against high voltage without resort to a plasma atmosphere interrupting mechanism. Aspects of a suitable auxiliary circuit are discussed in a paper by Greenwood and Lee, Paper T 72 107-6 IEEE Winter Power Meeting N.Y., January 1972.
Also among the prior art are papers that discuss related switching concepts, including a paper by J. Teno, O. K. Sonju, and J.M. Lontai, of AVCO Everett Research Labs, Inc., entitled "Development of a Pulsed High-Energy Inductive Energy Storage System," published August 1973. The work was done for the Air Force Aeropropulsion Lab and carries publication No. AD 766 518. Attention is particularly called to Chapter 7. A second related paper by C. E. Swannack, R. A. Haarman, J. D. G. Lindsay, and D. M. Weldon of the Los Alamos Scientific Laboratory is entitled "HVDC Interrupter Experiments for Large Magnetic Energy Transfer and Storage Systems." This paper was presented during the Sixth Symposium on Engineering Problems of Fusion Research, San Diego, Calif., November 1975.